Browsing by Author "Yoon, M"

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Embargo
Performance improvement of a cross-flow air turbine for oscillating water column wave energy converter by nozzle and blade optimization
(Elsevier Ltd, 2025-01-15) Baddegamage B.H.B.P.D; Bae, S.J; Jang, S.H; Gunawardane S.D.G.S.P; Lee, Y.O; Kim, K; Yoon, M
The global pursuit of renewable energy solutions has highlighted the potential of wave energy converters (WECs), particularly oscillating water column (OWC) systems, as viable clean energy sources. This study focuses on optimizing a cross-flow air turbine (CFAT) through comprehensive numerical simulations, aimed at enhancing its performance as the power take-off system in OWC applications. The influences of various geometrical parameters, such as including nozzle entry arc angle, nozzle starting angle, and angle of attack, on the performance of the CFAT are investigated. The optimized turbine model achieves a peak efficiency (η) of 0.71 in unidirectional flow at a flow coefficient (Φ) of 0.41, representing a significant improvement over the reference model (η = 0.61 at Φ = 0.29). In addition, the performance of the optimized CFAT is evaluated under regular wave conditions, simulating the bidirectional flow typical of real-world OWC applications. Although the peak efficiency in reciprocating flow slightly decreases, shifting to 0.68 at Φ = 0.53, the turbine maintains a high mean efficiency throughout the operating cycle. The results demonstrate that the optimized CFAT model provides robust performance in both unidirectional and bidirectional flows, making it a promising candidate for enhancing the efficiency of OWC-based WECs.
Embargo
Performance Improvement of Crossflow Air Turbines for Wave Energy Conversion in Oscillating Water Columns: A CFD Study
(SLIIT, Faculty of Engineering, 2024-10) Baddegamage, B.H.B.P.D.; Lee, Young-Ho; Gunawardane, S.D.G.S.P.; Yoon, M
The coastal countries have a valuable renewable energy source in the form of ocean waves, which, if harnessed effectively using wave energy converters (WEC), could significantly enhance their electrical energy supply. Numerous technologies have been researched, put forth, examined, and sometimes tested in real ocean conditions at full scale. One of the most promising WECs is the oscillating water column (OWC), which has a modest number of moving parts that are all above the water level with a relatively simple mechanism. Although the Wells turbine is a widely used power takeoff (PTO) system of OWC, having higher peak efficiency than the crossflow air turbine (CFAT), it shows a narrow operational flow range. This operational flow range issue could be addressed by deploying CFATs. Only a few researches have been conducted on the CFAT as the PTO for OWCs. The present study focuses on numerical model-building and validation using the available experimental data to investigate the performance characteristics for optimized nozzle shapes for CFAT. For the base model, numerical results are compared to experimental data for validation. The geometry of the nozzle is optimized to achieve maximum efficiency under steady-state conditions. The nozzle entry arc angle is varied between 90° to 150°. The optimized model reached a peak efficiency of 68% with a steady high efficiency for broader operating conditions (broader flow range). Therefore, the proposed design addresses the issue of the narrow band of the Wells turbine while potentially improving the efficiency of the existing CFAT model.
Open Access
Self-starting characteristics and dynamic response of a free-spinning cross-flow air turbine for oscillating water columns under irregular wave conditions
(Elsevier Ltd, 2026-02-24) Baddegamage B.H.B.P.D; Bae, S.J; Gunawardane S.D.G.S.P.; Lee, Y.H; Kim, K; Yoon, M
The cross-flow air turbine (CFAT) has been proposed as a self-rectifying device for oscillating water column (OWC) wave energy converters as an alternative to conventional Wells and impulse turbines. While previous studies have primarily focused on steady or regular flow conditions, the self-starting behavior and transient response of a free-spinning CFAT under irregular, bidirectional inflow representative of realistic sea states have not yet been investigated. This study presents a fully transient computational fluid dynamics analysis of a free-spinning CFAT operating under irregular airflow conditions derived from the JONSWAP spectrum. The simulations were performed under no-load conditions to isolate the intrinsic aerodynamic torque generation and evaluate self-starting capability. The effects of significant wave height and spectral peak period on turbine startup and unsteady aerodynamic response were systematically examined in both the time and frequency domains. The CFAT consistently initiates rotation without external assistance and reaches quasi-steady operation within 25–30 oscillation cycles. For significant wave heights ranging from 0.0375 m to 0.05 m, the mean instantaneous efficiency varies between 0.24 and 0.52, while efficiencies between 0.30 and 0.59 are obtained for spectral peak periods from 1.50 s to 1.88 s. Furthermore, wave-grouping effects play a decisive role in accelerating the turbine toward its equilibrium speed. Torque and pressure fluctuations closely follow the inflow velocity profile, with hysteresis-like behavior observed during flow reversals. These findings confirm the CFAT's suitability for practical OWC applications, demonstrating robust self-starting and stable performance under irregular conditions.